The present invention relates to a fuel cell system, and more specifically, to a fuel cell system that improves power generation efficiency and reduces weight and size.
As environment-friendly electric automobiles, automobiles having polymer electrolyte fuel cell systems have been developed. A fuel cell system employs a fuel cell formed by laminating power generation cells. Each power generation cell includes a hydrogen ion conductive solid polymer electrolyte membrane. A carbon anode supporting a platinum catalyst is laminated on one side of the solid polymer electrolyte membrane, and a carbon cathode supporting a platinum catalyst is laminated on the other side. A gas passage forming member is laminated on the surface of each of the carbon electrodes. The gas passage forming member forms a gas passage for supplying reaction gas to the carbon electrode. The gas passage forming member is formed of a metal lath. A flat plate shaped separator is laminated on the surface of each gas passage forming member.
Hydrogen gas as fuel gas is supplied to the anode. Air (oxygen gas) as oxidation gas is supplied to the cathode. At the anode, the hydrogen gas is ionized. Hydrogen ions permeate the solid polymer electrolyte membrane to move to the cathode. The hydrogen ions react with oxygen at the cathode, generating water. Some of the generated water moves from the cathode and permeates the solid polymer electrolyte membrane, and then flows into the anode. Electrons at the anode move to the cathode through an external load. The series of these electrochemical reactions extracts electric energy.
Japanese Laid-Open Patent Publication No. 2005-332674 discloses one type of the above described fuel cell. This fuel cell has a fuel cell stack accommodated in a stack case. The fuel cell stack has cell modules with both ends supported by end plates. One of the end plates has a terminal, from which a high voltage is supplied to an electric motor. The other end plate is formed of an electrical insulation material. Pipes for supplying and discharging hydrogen gas, air, and coolant are independently connected to this end plate made of the electrical insulation material. These pipes require a large installation space, which hinders reduction in size and weight.
To solve the above present problems, Japanese Laid-Open Patent Publication No. 2008-177100 has proposed a fuel cell system. According to the publication, a fuel cell stack incorporates a plurality of manifolds. Inlets and outlets of the manifolds are formed on one side of the fuel cell stack. A resin piping member is attached to the fuel cell stack. The piping member has a plurality of fluid passages at parts that contact the cell stack. The fluid passages extend to positions that correspond to the inlets and outlets of the manifolds. The fluid passages include a hydrogen inlet passage, a hydrogen outlet passage, an air inlet passage, an air outlet passage, a coolant inlet passage, and a coolant outlet passage. With the piping member attached to one side of the fuel cell stack, each of the fluid passages is connected to the corresponding one of the inlets and outlets of the manifolds.
As described above, the piping member of the fuel cell system disclosed in Japanese Laid-Open Patent Publication No. 2008-177100 is a single unitized member, which simplifies the structure of the system. However, the piping member still has a plurality of independent pipes forming the fluid passages. Thus, it is impossible to cool air flowing through the air inlet passage using coolant flowing through the coolant inlet passage. The temperature of air supplied to the air inlet passage by a compressor therefore cannot be lowered, hindering the electrochemical reaction between hydrogen and oxygen. This prevents the power generation efficiency from being improved. Further, since the pipes are arranged at predetermined intervals, a relatively large space is required for each pipe, the weight and size of the pipes cannot be reduced.